Method and systems for buffering anesthetic cartridges with buffering solutions

ABSTRACT

An anesthetic cartridge is adapted to receive a volume of buffer by displacing a plunger in one end of the anesthetic cartridge inwardly so that addition of the buffer volume will not displace the plunger excessively beyond the end of the cartridge body. By properly determining the amount of buffer volume required to raise the pH of the anesthetic to a target value, the degree of inward displacement of the plunger can be determined and the cartridge can be used with a system for delivering a precise amount of buffer solution having a known pH into the cartridge to raise its pH, just before the anesthetic is delivered to the patient.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of provisional application 61/341,916, filed on Apr. 7, 2010, the full disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods and apparatuses for buffering anesthetic cartridges. More specifically, the present invention relates to methods and devices for delivering an amount of buffering solution to an anesthetic cartridge to achieve a target pH with a minimum of waste.

Cartridges of local anesthetic commonly used in dentistry (herein “dental anesthetic cartridges”) are filled nearly completely with anesthetic where the cartridge's plunger is located at or near the end of the cartridge. The anesthetic is typically delivered by loading the cartridge into a breach in a reusable stainless steel dental syringe to which a disposable hypodermic needle has been attached. After the anesthetic has been delivered and the dental procedure is complete, the needle and the anesthetic cartridge are discarded and the syringe is steam sterilized. Anesthetic cartridges are sometime used by dentists in other automated delivery systems for instance in the system disclosed in U.S. Pat. No. 7,896,833.

The solutions in most dental anesthetic cartridges are acidic, and it is beneficial to raise the pH of the anesthetic, or buffer the anesthetic, just prior to delivery, in order to reduce injection pain, improve profundity, reduce anesthetic failure, and speed the onset of analgesia. Buffering the anesthetic inside the cartridge immediately prior to delivery allows the dental practitioner to subsequently deliver the anesthetic using his or her normal technique and cartridge-based delivery system, which is convenient.

Such a buffering process that adds buffering solution to a sealed anesthetic cartridge, however, is problematic since adding the buffer to the volume of anesthetic already in the cartridge displaces the cartridge's plunger, potentially pushing the plunger partially or fully out of the end of the cartridge.

A method and apparatus for buffering anesthetic cartridges that prevent such plunger displacement are disclosed in commonly assigned U.S. patent application Ser. No. 12/406,670, the full disclosure of which is incorporated herein by reference. Buffer from a fluid container is added to the dental anesthetic cartridge via a transfer tube while simultaneously the same amount of anesthetic is removed from the cartridge via an exhaust tube.

A method and system of buffering the anesthetic cartridge without the need to exhaust anesthetic would be beneficial as it would reduce waste, eliminate the need to capture the exhausted anesthetic, and simplify construction of the buffer mixing apparatus. At least some of these objectives will be met by the inventions described below.

2. Description of the Background Art

Glass cartridges for storing and delivering anesthetic solutions and delivery systems for the same are described in U.S. Pat. Nos. 3,556,099, 4,472,141, and 5,368,572. Commonly owned application Ser. Nos. 12/406,670; 12/766,259; 12/833,356; and 12/833,702, all of which are fully incorporated herein by reference, are also related to similar technologies.

SUMMARY OF THE INVENTION

The present invention provides methods and systems for buffering anesthetics with buffer solution to raise the pH in order to improve anesthetic effectiveness, speed anesthetic onset time, and reduce patient discomfort. The method and systems are useful with a variety of slightly acidic anesthetics, including amide local anesthetics and amine local anesthetics, such as Lidocaine and Articaine, which are commonly used in dental procedures. The methods and systems of the present invention, however, are not intended to be limited to those particular examples and may find use with a wide variety of anesthetic solutions, buffer solutions, different medical procedures, and the like.

In a first aspect of the present invention, an anesthetic is held in a cartridge having a pierceable septum at one end and a plunger at the other end, said cartridge being of the type intended to be placed into a syringe for advancing the plunger to deliver the anesthetic through a the syringe's hypodermic needle that is driven through the cartridge's septum in the process of loading the cartridge into the syringe's breach. The method comprises determining a volume of buffer needed to adjust pH of a volume of the anesthetic to a target value, typically being at least 7, often being at least 7.3. An anesthetic cartridge containing the volume of anesthetic is provided, where the plunger is set back from an end of the cartridge by a distance sufficient to allow the cartridge to receive the volume of buffer without displacing the plunger beyond the end of the cartridge. The volume of buffer may then be introduced into the cartridge to achieve the desired target pH without displacing the plunger beyond the cartridge end.

In preferred aspects of the method, the cartridge is typically prepared at a central manufacturing facility and distributed from the facility to a plurality of local users, where each of the local users will then be able to inject the desired volume of buffer. The cartridges may thus be prepared in large quantities of identical cartridges where the plunger is set back by identical distances. The users will know that they can reliably introduce a predetermined volume of buffer into those cartridges without the risk of displacing the plunger beyond an acceptable position within the cartridge. The users are then able to mix the buffer with the anesthetic immediately prior to a procedure, where at least a portion of the buffered anesthetic can thus be delivered to the patient within 30 minutes of mixing to ensure that the buffered anesthetic is fresh and not degraded.

In further preferred aspects of the method, the internal volume of the anesthetic cartridge will be in the range from 1.45 ml to 2.3 ml, often from 1.7 ml to 1.8 ml, usually being 1.8 ml. The anesthetic fill volume is usually in the range from 1.15 ml to 2.2 ml, often from 1.5 ml to 1.7 ml, more usually in the range from 1.55 to 1.65 ml, and the buffer volume is the range from 0.1 ml to 0.35 ml, typically being in the range from 0.15 ml to 0.25 ml. In still other aspects, the local anesthetic may contain may contain vasoconstrictor such as Epinephrine.

The present invention further provides a system for preparing a buffered anesthetic comprising an anesthetic cartridge and a buffer container. The anesthetic cartridge has a septum at one end and a plunger at the other end, and is filled with a volume of anesthetic. The buffer container holds a volume of buffer, where the volume of buffer is selected to raise the pH of the anesthetic volume to a target pH (where the volume of buffer can be calculated based on the volume of anesthetic and expected pH of the buffer). In particular accordance with the present invention, the plunger in the anesthetic container is set back from an end of the anesthetic cartridge by a distance sufficient to allow the cartridge to receive the buffer volume without displacing the plunger beyond the end of the cartridge. The volume of buffer in the buffer container will be precisely that volume which has been calculated to raise the pH of the anesthetic volume in the anesthetic cartridge in the desired amount to the target pH.

The buffer may comprise a sodium bicarbonate solution having a nominal pH and an actual pH, where the actual pH (that pH which would be measured in the cartridge immediately prior to use) is within ±0.10 of the buffer solution's nominal pH.

In yet another aspect of the present invention, an inventory of anesthetic cartridges will comprise a plurality of identical anesthetic cartridges, each having a plunger at one end, a septum at the other end, and being partially filled with an anesthetic solution. The plunger in each container is spaced away from the plunger end of the cartridge by a distance of at least 10% of the container length, sometimes being at least 12%, and, in at least some instances, being greater than 15%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional and aesthetic cartridge having a plunger disposed near a plunger end of the cartridge in order to maximize the volume of an anesthetic within the cartridge.

FIG. 2 illustrates an anesthetic cartridge in accordance with the principles of the present invention where the plunger has been moved away from the plunger end of the cartridge in order to provide a potential volume within the container for receiving a selected volume of upper solution.

FIG. 3 illustrates a method according to the present where buffer and a buffer container is being transferred into the anesthetic volume within the anesthetic cartridge.

FIG. 4 illustrates a system according to the present invention where an aesthetic cartridge, such as that shown in FIG. 2, is combined with a buffer container, where the buffer container includes a single dose or volume of buffer, where that dose or volume is intended to raise the pH of the anesthetic within the cartridge to the target pH.

FIG. 5 illustrates an inventory according to the present invention comprising a plurality of identical anesthetic cartridges having the set-back plungers of the present invention.

DETAILED DESCRIPTION

The present invention provides methods and systems for using a dental anesthetic cartridge as a mixing vessel for combining an anesthetic in the cartridge with a buffering solution from a separate container. In an embodiment of the current invention, the problems associated with plunger displacement during pH buffering are overcome by configuring a dental anesthetic cartridge for use with a system that delivers a precise amount of buffering solution to the cartridge, using the anesthetic cartridge itself as the mixing chamber to combine the buffer solution and the anesthetic solution, while displacing the plunger no more than a precise amount calculated to allow the plunger to move a predetermined distance sufficient to accept the buffer solution without displacing the plunger past the end of the cartridge.

A conventional anesthetic cartridge 10 is illustrated in FIG. 1 and includes a glass tube 12, a plunger 13 at one end of the glass tube 12, a pierceable septum 14 at the other end of the glass tube, and a cap 15 covering the septum 14. An interior volume 16 of the glass tube 12 is filled with an anesthetic solution, typically as described above. As can be seen in FIG. 1, if any significant volume of buffer were to be added to the volume of anesthetic which fills the interior 16 of the glass tube, the plunger 13 would be displaced outwardly, as shown in broken line in FIG. 1. While the displaced plunger 13 in FIG. 1 is only partially displaced, it would be appreciated a slightly greater volume of buffer would completely dislodge the plunger from the tube, allowing the anesthetic and buffer to spill. Even if the plunger 13 were only slightly displaced from the glass tube 12, it is likely that the cartridge 10 would still not be useable since it would be difficult, if not impossible, to place the cartridge into most syringe assemblies intending to receive the cartridge, where the plunger 13 is expected to be flush within the glass tube 12.

Thus, in accordance with the present invention, the plunger 13 will be initially displaced inwardly from the end of the cartridge, as shown in FIG. 2. If the dimensions of the glass tube 12 are identical to those of the conventional anesthetic cartridge in FIG. 1, then the volume of anesthetic within the cartridge will have been reduced somewhat, but there will be sufficient displacement room for the plunger 13 to move to the left, as shown in FIG. 2, in order to accommodate a desired volume of buffer to be introduced to the cartridge, as shown in FIG. 3.

As shown in FIG. 3, a buffer container 17 is used to transfer buffer to the interior 16 of the anesthetic cartridge 10. For example, a transfer tube 18 may be inserted through the septum 14 of the anesthetic cartridge 10 at one end and inserted through the septum 16 of the buffer cartridge 17 at its other end. Thus, a transfer path exists between the buffer solution and the anesthetic solution. Buffer cartridge 17 may itself have a plunger (not illustrated) which allows transfer of the desired buffer volume to the interior 16 of the anesthetic cartridge 10 which will result in displacing the plunger 13 to the position shown in broken line in FIG. 3. The volume will be calculated in this method such that the target pH adjustment of the anesthetic solution will be achieved without displacing the cartridge 13 out from the end of the glass tube 12.

In another embodiment, the cartridge 10 identical to those described with respect to FIGS. 2 and 3 may be combined with a buffer cartridge 27 adapted to deliver a “unit dose” of the buffer to the interior of the anesthetic cartridge 10, for example, by pressing on plunger 28 after inserting needle 29 through the septum of the anesthetic cartridge 10. The buffer cartridge 27 will exhaust the buffer therein and can then be disposed of in a manner compatible with the presence of the needle.

With reference to FIG. 5, an inventory 50 of anesthetic cartridges 10 may be prepared with inwardly displaced plungers, as illustrated in FIGS. 2 and 3 above. The dimensions of the cartridges 10 and volumes of anesthetic held in each cartridge will preferably be identical so that the cartridges may be distributed to end users and the end users may be able to combine the anesthetic solutions with known (predetermined) amounts of buffer to achieve the desiring buffering effect. Specific techniques and volumes for combining buffers having precisely controlled pH values are described in the commonly owned, co-pending U.S. patent applications incorporated by reference above. The inventories of containers 10 will frequently be packaged within boxes or other containers for holding the plurality of containers together for shipment to individual users or groups of users.

In one example, a health care practitioner could use the methods and system of the present invention to prepare anesthetic cartridges with anesthetic solutions at a pH that is close to physiologic, as follows. An anesthetic cartridge sized to contain 1.8 ml of anesthetic (the typical dental anesthetic cartridge size used in the United States), and the anesthetic solution in the cartridge is 2% lidocaine with epinephrine in a concentration of 1:100,000, and the starting pH of the anesthetic solution is 3.5, and the buffering solution is 8.4% sodium bicarbonate, and the pH of bicarbonate solution is 7.70, then the amount of buffering solution that would be added to the anesthetic cartridge would be 0.18 ml. In this example, the anesthetic cartridge would be configured during manufacture with the plunger in a position so that the fluid volume in the filled cartridge would be 1.62 ml, which is 0.18 ml less than the 1.8 ml maximum that the cartridge would normally hold. A precision delivery device would deliver 0.18 ml of the bicarbonate solution into the anesthetic cartridge via the transfer tube. The plunger would displace outward but not beyond the end of the cartridge, and the anesthetic and the bicarbonate solutions would mix inside the anesthetic cartridge. The anesthetic cartridge would be disconnected from the transfer tube, and then the anesthetic cartridge would immediately be used in an anesthetic delivery system, such as a reusable dental syringe.

In an additional embodiment, where it is desirable that the inside portion of glass tube 12 that is to the left of the plunger 13 in FIG. 2 is kept in a sterile condition prior to use, after sterilizing this portion of the glass, a covering membrane 20 would be attached. Membrane 20 could be pierceable, so that the harpoon or similar devices that allow for aspiration during anesthetic deliver could still function. Membrane 20 could also be removable by the practitioner immediately before the cartridge is buffered or used.

While the above is a description of a preferred embodiment of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting the scope of the invention which is disclosed. 

1. A method for buffering an anesthetic in a cartridge having a septum at one end and a plunger at the other end, said method comprising: determining a volume of buffer needed to adjust the pH of a volume of the anesthetic to a target value; providing an anesthetic cartridge containing the volume of anesthetic wherein the plunger is set back from an end of the cartridge by a distance sufficient to allow the cartridge to receive the volume of buffer without displacing the plunger beyond the end of the cartridge; and introducing the volume of buffer into the cartridge.
 2. A method as in claim 1, wherein the cartridge is prepared at a central manufacturing facility and the cartridges are distributed to a plurality of local users, wherein the users inject the buffer.
 3. A method as in claim 2, wherein the users inject the buffer prior to a procedure, in order to produce buffered anesthetic for use in the procedure.
 4. A method as in claim 3, wherein at least a portion of the buffered anesthetic is injected into a patient within 2 minutes of introducing the buffer.
 5. A method as in claim 1, wherein the anesthetic originally has a pH below 6.0 and the volume of buffer raises the pH of the buffered anesthetic to at least 7.0.
 6. A method as in claim 5, wherein the volume of buffer increases the pH to at least 7.3.
 7. A method as in claim 1, wherein the local anesthetic is an amide local anesthetic.
 8. A method as in claim 1, wherein the local anesthetic is an amine local anesthetic.
 9. A method as in claim 1, wherein the local anesthetic is lidocaine.
 10. A method as in claim 1, wherein the local anesthetic is articaine.
 11. A method as in claim 1, wherein the local anesthetic contains a vasoconstrictor.
 12. A method as in claim 11, wherein the vasoconstrictor is epinephrine.
 13. A method as in claim 1, wherein an internal volume of the anesthetic cartridge is in the range from 1.45 ml to 2.3 ml, the anesthetic volume is in the range from 1.15 ml to 2.2 ml, and the buffer volume is in the range from 0.1 ml to 0.35 ml.
 14. A system for preparing a buffered anesthetic, said system comprising: an anesthetic cartridge having a septum at one end and a plunger at the other end, wherein said cartridge is filled with a volume of anesthetic; and a buffer container holding a volume of buffer selected to raise the pH of the anesthetic to a target pH; wherein the buffer container is adapted to transfer the buffer volume to the anesthetic cartridge and wherein the plunger is set back from an end of the anesthetic cartridge by a distance sufficient to allow the cartridge to receive the buffer volume without displacing the plunger beyond the end of the cartridge.
 15. A system as in claim 13, wherein the anesthetic cartridge has an internal volume in the range from 1.45 ml to 2.3 ml, the anesthetic volume within the cartridge is in the range from 1.1 ml to 2.2 ml, and the buffer volume is in the range from 0.10 ml to 0.35 ml.
 16. A system as in claim 15, wherein the buffer comprises a sodium bicarbonate solution having a nominal pH and an actual pH which is with ±0.1 of the nominal pH.
 17. An inventory of anesthetic cartridges comprising: a plurality of identical containers each having a plunger at one end, a septum at other end, and being partially filled with an anesthetic solution; wherein the plunger in each container is spaced away from the plunger end of the cartridge by a distance of at least 10% of the container length. 